INTRODUCTION health fish managements may result in considerable
Aeromonas hydrophila and other motile aeromonads, benefit of aquaculture production [3].
such as A. veroneii bv. Sobria, are Gram-negative bacteria Different types of vaccines, such as whole cell, outer
and are also part of the normal flora of aquatic membrane proteins, extra-cellular proteins and
environment. Aeromonas hydrophila is known to be one lipopolysaccharides (LPS) have been investigated against
of the most important bacteria associated with the A. hydrophila [4-6]. Injection or immersion vaccination
diseases in marine and freshwater fishes. It can cause with heat or formalin-inactivated bacterins also provides
several health interferes in both fish and humans, some protection against A. hydrophila [4, 7]. LPS is
including tail and skin rot and fatal hemorrhagic derived from Gram-negative bacteria and consists of lipid
septicemias in fish and soft-tissue wound infection and A, core polysaccharide and O-specific chain. The lipid A
diarrheic diseases in humans [1]. portion of an LPS is known as an endotoxin and is
Nowadays, most of the cultured fish diseases are responsible for most of the immunomodulatory effects of
treated with drugs, such as antibiotics, anti-parasite, etc. LPS [8]. The fish immunized either intramuscularly or
The chemotherapeutic actions are particularly effective intraperitoneally with vaccine showed protection
when used as early as possible and also have a wide against challenges [9]. Moreover, agglutinating antibody
spectrum of pathogen control. However, several was recognized in the serum of carp immunized with
difficulties are often encountered by chemotherapy. A. hydrophila bacterin following a second immersion with
For instance, the drugs are expensive, the resistant strains this vaccine. However, the fish vaccinated either orally or
of pathogens are easily induced in water and the drug by immersion showed questionable protection [10].
residues which may deposit in fish body may introduce The present study aimed to prepare formalin and
potential hazards to the public health as well as the heat-killed whole cells, LPS vaccines of A. hydrophila and
environment [2]. In order to decrease the side effects of a bivalent vaccine of A. hydrophila and A. veronii bv.
chemotherapy, using of vaccines, accompanied with good sobria for direct immersion vaccination of rainbow trout.